Fertility rates in the United States have fallen below the replacement rate, and are beginning to diverge substantially from what women state as their reproductive goals. Whereas, women say they want on average 2.7 children, current rates show they will probably have no more than 1.8. That gap is the highest it has been in 40 years.

Explanations for the drop in fertility include postponing marriage, having less sex, and the decline in pregnancy rates among young women. That low rate now affects women throughout their 20s and early 30s. In the background is the fact that contraceptive technology has improved while reproductive technology has not.

Falling fertility rates might portend trouble for Social Security, a graying population in need of care, and stagnant economic growth.